Unity is an integrated authoring tool for creating 3D video games or other interactive content such as architectural visualizations or real-time 3D animations. Unity is similar to Director, Blender game engine, Virtools or Torque Game Builder in the sense that an integrated graphical environment is the primary method of development.
Simple

With Unity 3, we've put tremendous effort on world building tools - so you can assemble and tweak your levels at the speed of thought.
Edit. Test. Play. With Unity, testing your latest idea is never more than a click away. This lets you drill down to find the fun, then polish it until it's perfect.
Target platform can be switched instantly, so you can develop from a single source for mobiles, web, PC/Mac, and consoles.

Powerful

We rewrote Unity's rendering pipeline so your games can look the best they can - and get a 50% performance boost on top.
Unity 3 brings Beast lightmapping and Umbra occlusion culling to the table - a key part of making games look great and run fast across all devices.
Design the perfect aural ambience with our new integrated audio filters and in-scene editing tools. Captivating your audience has never been easier.

System Requirements for Unity iOS Authoring
An Intel-based Mac
Mac OS X "Snow Leopard" 10.6 or later
The rest only depends on the complexity of your projects!